1. The Field of the Invention
The present invention relates to cable modems. More specifically, the present invention relates to an interface between the physical layer and the data link layer of the cable modem protocol stack and to placing data on and retrieving data from a cable modem.
2. The Prior State of the Art
The Internet is a worldwide interconnection of networks over which computers can exchange information. Never before have human beings had access to so much information from the comfort of their own homes or offices. For Wide Area Networks (WANs) such as the Internet, a computer typically employs a modem to send information to and receive information from other connected computers. There are many types of modems each corresponding to a specific type of medium used to deliver this information.
One common modem uses Plain Old Telephone Service (POTS) to send and receive information. POTS modems have an advantage in that they use a transmission medium that is available by just connecting the modem with the nearest phone jack. Thus, the POTS modem does not require expensive capital investment to set up a connection to the Internet. Although POTS modems are easy and inexpensive to connect to the Internet, the transmission speeds available over plain old telephone service are relatively slow. Currently, POTS modems are capable of information exchange at up to only 56,000 bits per second (bps) or approximately 0.056 megabits per second (Mbps). While faster POTS modems may eventually become available, it is not currently anticipated that POTS modems can become significantly faster due to physical limitations in the telephone lines themselves.
Telephone companies are now offering services that bypass the relatively slow telephone lines to establish a more direct connection to the Internet. For example, T1 connections permit information exchange in the megabit per second range. T2 and T3 connections allow for even higher speed information exchange. Currently, T1, T2 and T3 connections respectively permit information exchange at approximately. 1.544 Mbps, 6.312 Mbps and 44.736 Mbps. Although these direct T1, T2 and T3 connections permit information exchange orders of magnitude faster than is available over plain old telephone service, they are typically much more expensive to obtain and/or maintain than plain old telephone service since each connection requires dedicated circuitry. Furthermore, telephone companies typically provide both the plain old telephone service and the T1, T2 and T3 connections. To facilitate free market competition, it would be desirable for a consumer to have alternative suppliers of Internet access.
A cable modem is a device that hooks up to the Internet through a cable system provided by a cable supplier. Assuming that the cable supplier facilitates Internet access as many cable suppliers are want to do, Internet access is obtained by plugging the cable modem into a cable connection that typically already exist (or may be readily installed) in many homes and business. Thus, the cost of connecting a cable modem to the Internet is relatively small compared to establishing T1, T2 and T3 connections since the extensive cable network that supports communication already exists. Thus, there is no need to establish extensive dedicated circuitry to support each new end user.
Furthermore, dialing into the Internet is not needed since data may be communicated to or from the end-user over the cable system without dialing into the cable system. A cable modem network is a connectionless system, whereas the telephone system is a connection oriented service. In a connectionless system, information is passed when information is available and the system resources are available to other users the rest of the time. In contrast, a connection oriented system sets up a connection which is set up and torn down for each communication. For instance, most internet users, when internet access is desired, must place a call to an Internet service provider to establish a connection. Once the connection is established, the user can access the internet. When the user is finished, the connection is terminated by hanging up. This is not the case with cable modems because a cable modem user has no need of dialing into an Internet service provider because the user appears to be connected at all times. The initial connection to the Internet is much faster compared to using plain old telephone service.
In addition, cable modems allow for much faster information exchange than is available over plain old telephone service. An individual cable modem end user may experience information exchange speeds of from 0.5 Mbps to 1.0 Mbps or more depending on the cable network architecture and traffic load. This represents a speed that is at least an order of magnitude faster than is currently available over plain old telephone service. Furthermore, cable information exchange speeds may be further increased due to future improvements in cable technology. Thus, cable modems provide a low cost, high-speed alternative for Internet access.
In a typical cable modem configuration, the cable modem is external to and separately addressable from the end user""s computer system. The end user""s computer is then connected to the cable modem using, for example, a network card. One reason for which the cable modem is external to the end-user""s computer is that the cable modem may have access control settings that are to be set by the cable operator, not by the end-user. For example, the cable operator may want to prohibit access to certain services unless the end-user has communicated a subscription to the cable indicating a willingness to abide by certain terms. Allowing the end-user to directly access and set these access control settings would bypass the very purpose for having the access control settings. Thus, having the cable modem be external to the end-user""s computer has the advantage of the cable operator retaining control of the access control settings within the cable modem.
Communication over a cable network using a cable modem is typically performed using a standard such as the well-known Data Over Cable Service Interface Specification (DOCSIS) 1.0 standard, which establishes uniform data transmission standards. The DOCSIS standard is managed by the Multimedia Cable Network System (MCNS), an organization formed by major cable operators.
Because the cable modem is external, the cable modem does not use the processing capability of the central processing unit (CPU) of the end user""s computer. Also, the cable modem does not share memory with the end user""s computer. Thus, the cable modem has its own CPU and memory which increases the cost of the cable modem.
Because the cable modem is typically external to an end user""s computer or other equipment and because the cable modem has controls which are set by the company providing the cable service, the development of cable modems has not been uniform. This non-uniformity has been a roadblock to the integration and interoperability of cable modems with, for example, a computer or a set top box. There are computers or other equipment which provide a cable modem in the same box, but the computer and the cable modem are not truly integrated because the cable modem and the computer do not share the same processor or memory.
In would be an advancement in the art to integrate a cable modem with a computer or a set top box or other equipment. Additionally, it would be an advancement in the art to provide an interface such that a cable modem of any manufacturer can be used in a particular computer or set top box and can be used in more than one cable network. Thus, what is desired is a computer system that integrates a cable modem with customer premises equipment in a manner that preserves the advantages of an external cable modem, reduces cost and standardizes the transfer of data from the cable modem to the customer premises equipment.
The present invention provides for integrating a cable modem with a customer premises equipment in a system where, in a preferred embodiment, the cable modem and the customer premises equipment share a processor and resources. As used herein, the term xe2x80x9ccustomer premises equipmentxe2x80x9d (CPE) refers to any electronic device, such as a computer, a set top box, or the like, that uses a cable modem to access network resources or communicate with other networked components.
Because a cable modem has typically been built as an external device related to computers, set top boxes and other equipment, manufacturers of cable modems have implemented cable modem protocol in varied manners when designing the cable modems. The present invention provides for integrating the cable modem with a CPE or a host, but the DOCSIS standard has not previously had any specifications for a cable modem that is integrated with a customer premises equipment (CPE) such as a computer or a set top box.
The protocol stack of a cable modem is related to the well-known open systems interconnection (OSI) model. The relevant layers include the physical layer (layer 1), the data link layer (layer 2), and the network layer (layer 3). The physical layer is primarily the hardware associated with the cable modem and the data link layer is typically represented by a media access controller layer. The network layer and higher layers essentially conform to standards of other networks and are not specific to cable modems.
The present invention defines an interface which serves to transfer data packets between the physical layer, which is represented by the cable modem, to a media access controller (MAC), which implements the data link layer. Because cable modems are not uniform, the present invention defines an interface to transfer the data packets between the cable modem and the MAC. In a sense, the interface, also referred to as the hardware abstraction layer, separates the functions of the hardware from the software. Thus, the interface performs a portion of the functions associated with each of physical layer and the data link layer. The interface permits cable modems to be used in any host computer having the hardware abstraction layer, so long as the cable modem complies with the requirements of the interface.
Through the interface, the media access controller controls the function of the cable modem. The interface handles the hardware specific functions of the media access controller and exports its services to the media access controller. In this manner, information can be transmitted, in a standardized method, from the cable modem to the media access controller. In addition, the hardware abstraction layer enables interoperability between various cable modems and host computers without the designers or manufacturers of the cable modems and host computers needing to understand the internal, and sometimes proprietary, features other components in the system.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.